With rapid popularization of a user equipment such as a mobile phone, the user equipment is playing a more and more important role in people's life. Other functions besides communication in the user equipment are being more and more widely used, for example, accessing to Wireless Local Area Network (WLAN) with the user equipment. Moreover, interfaces such as infrared, BLUETOOTH, and Universal Serial Bus (USB) gradually become a standard configuration of the user equipment, in order to facilitate the communication link, data exchange and the like between the user equipment and other equipment. Particularly, the BLUETOOTH headset is becoming more and more widely used. Both the WLAN system and the BLUETOOTH system work at the Industry, Science and Medical (ISM) frequency band. For example, the frequency band 2400 MHz-2483.5 MHz is one of the international ISM frequency bands, and is also one of the ISM frequency bands used most frequently.
In a case in which the frequency band on which the communication between the user equipment and a base station is based is close to or a multiple of the frequency band on which the communication between the user equipment and other equipment is based, those two types of communications may interfere with each other. For example, the advanced Long Term Evolution (LTE) system in the wireless communication system is one of the system beyond 3G (beyond IMT-2000). According to the LTE standard series [36.101], the LTE system may work at several frequency bands. Among these LTE working frequency bands, some frequency bands are adjacent to the ISM frequency band, such as the frequency band 40 for deploying a LTE Time Division Duplexing (TDD) system, 2300 MHz-2400 MHz, and the frequency band 7 for deploying a LTE Frequency Division Duplexing (FDD) system, uplink 2500 MHz-2570 MHz, downlink 2620 MHz-2670 MHz. If a certain LTE user equipment works at the above frequency band while the WLAN system or the Bluetooth system in this user equipment is in an activated state, then due to adjacent frequency band leakage, the LTE system and the ISM system (WLAN system, the Bluetooth system and the like) which work in the adjacent frequency bands in this user equipment may interfere with each other, and may even fail to communicate because of too high a bit error rate.
A conventional approach to resolve this problem is to provide a transmission filter with higher performance both in the transmission side (such as the LTE system) for communication with the base station on the user equipment and in the transmission side (such as the ISM system) for communication with other equipment on the user equipment, so as to decrease the adjacent frequency band leakage as much as possible. The disadvantage of this approach is that the cost of the user equipment will be significantly increased.